All information on this page is copied material from Gulvfakta, which is a technical reference material, Source: Gulvfakta

Tiled floors are floors covered with ceramic tiles or natural stone. Ceramic tiles are made from several types of clay, quartz sand, etc. as after kneading and possibly addition of small amounts of auxiliaries and dyes is shaped, dried and finally burned. Natural stone tiles are made from several different types of stone, e.g. marble and granite. In the following, only the term tiles is used.

You can also see our selection of tiles and clinker for both inside and outside. Introduction
Material types
General conditions
Laying methods
Wet room
Underfloor heating
Checklist when choosing tiled floors

All information on this page is copied material from Gulvfakta, which is a technical reference material, Source: Gulvfakta Introduction
Tile floors are widely used in homes, industrial buildings and other places where special properties are required, such as great robustness, waterproofing of the construction or easy and efficient cleaning. Tiles are supplied in a large number of formats from mosaic pins, (ie tiles with side lengths below 100 mm) to large format tiles of 500 x 500 mm or larger. The thickness is most often 6-10 mm, but there are both thicker and thinner tiles. A tiled floor can be made with many different types of products and in many patterns.

This section discusses:
• Material types
• General conditions
• Laying - Substrate
• Laying methods
• Joints
• Wet room
• Underfloor heating
• Cleaning Material types
Ceramic tiles
Ceramic tiles are marketed in several variants both with and without glaze and in many different colours, including with applied motifs.

The tiles can be divided according to their production method into:
Wet pressed, which is produced by extruding a relatively moist mixture.
Dry pressed, which is produced by pressing a relatively dry mixture into molds under high pressure. A special type of dry-pressed tiles are tiles/faience tiles, which are produced by a special composition of the raw materials (high kaolin content). In general, dry-pressed tiles are dimensionally stable, stronger and less water absorbent than wet-pressed ones. However, earthenware tiles are relatively water absorbent. To provide better walking safety, the surface of the tiles can be made plain or with different embossments.

The properties of the tiles are determined by the composition of the clay mixture, the firing temperature and whether the tile is glazed or not. In general, higher firing temperatures will result in the densest and thus least absorbent tiles. The hardest fired tiles, which are characterized by having a hard shard, and by being sonorous when you hit them together, are also called clinker. They have a greater volume and strength and a smaller pore volume than the other tiles. Particularly hard-fired (stoneware) tiles are called porcellanato or granito tiles. They are distinguished by having particularly low water absorption and are therefore suitable in places where a large water impact is expected.

Fig. 1. Ceramic tiles

Natural stone tiles
Natural stone tiles are marketed in a large number of stone types which can be supplied with different surface treatments, for example the following:
Honed - graduated between coarse and fine. The structure of the surface is indicated by the grain size of the abrasive used.
Polished .
Cleft - i.e. split along natural fracture lines in the stone.
Jet-burnt - i.e. a thermal treatment of the surface.
The most important natural stones for floor coverings are the hard types such as granite and Nordic quartzite-slate types, softer sedimentary types such as limestone and sandstone and marble.

Granite is the term for a hard igneous rock, i.e. formed by the cooling of molten magma. Within the stone industry, the term granite is also used for individual rock types, which geologically are not granites. Extremely high pressures can transform the granite into a so-called metamorphic rock, which sometimes has a more striated appearance. The correct term for this type of rock is (granitic) gneiss, but in everyday speech the term granite is still used.
Sandstone is a type of sedimentary rock. Sandstone is formed from loose quartz sand, i.e. pure quartz, which may be composed of quartz or calcite. If the stone is cemented together with quartz, a solid and wear-resistant stone is obtained, while cementing with calcite, i.e. a lime-bound sandstone, gives less strength.
Limestone is a type of sedimentary rock. Limestone usually consists of cemented shells or skeletons of living organisms, i.e. the predominant minerals are usually calcite and dolomite. The carbonate minerals dissolve quite slowly in acidic environments, e.g. under the influence of certain cleaning agents.
Marble is a metamorphic rock formed from limestone that has been exposed to pressure and temperature. Due to the content of different minerals, marble can vary greatly in colour.
Basalt is dark to black igneous rock. Basalt is by far the most widespread type of rock in the earth's crust and forms the majority of the ocean floor and is also found in large areas of India, South America, Greenland, Iceland, etc. Basalt is dense and fine-grained, but is often fractured and difficult to exploit.
Slate is formed by the hardening of clay. First, shale is formed, which, when subsequent layers are superimposed, is exposed to pressure, whereby the shale clay is converted into shale. A decisive difference between slate and limestone/marble is slate's ability to split in a certain direction. Slate is often delivered with a split surface, but can usually also be delivered matt-ground.
Quartzite slate is the term for slate-like quartz-rich sandstone, which, due to a high mica content, is fissile just like slate.

Fig. 2. Natural stone tiles General conditions

Tiles have very different properties, e.g. depending on material composition and, in the case of ceramic tiles, production method and firing temperature. Tiles must therefore be chosen so that their properties match the intended use. Tile floors can be considered as fire-suitable class G floor coverings. The walking comfort and step sound absorption of tiled floors is poor, as tiles and their substrate usually consist of hard materials.

Tile floors have high thermal conductivity and heat capacity (heat accumulation capacity). They can feel cold to walk on because the heat is quickly conducted away from the foot. In general, tiles in themselves can be considered fairly resistant to the effects of chemicals. However, care must be taken with basalt and lime-bound natural stones, including marble, which cannot tolerate acidic chemicals, e.g. acidic cleaning agents. The joints in tiled floors, on the other hand, are not normally resistant to chemicals, so if chemical resistance is required, special joint mortars must be used. The flatness that can be achieved by a tiled floor depends on the flatness of the substrate, whether the tiles are delivered calibrated, i.e. with the same thickness everywhere, and of the surface flatness of the individual tiles. The tolerances will normally be ± 2 to ± 3 mm on a 2 m straight piece of wood.

In addition, the joints may differ in level from the surface of the tile itself. Because of the tolerances, it is usually not necessary to install tiled floors horizontally in wet rooms, etc., as this can lead to the appearance of gaps and thus the risk of water standing on the floor. Ceramic tile floors will not normally be surface treated, while certain natural stones are treated to prevent the penetration of grease and dirt and to have a more cleanable surface. Refer to the supplier's instructions for the current product. Tiles used as flooring in wet rooms must be able to withstand the effects of water and high humidity. Tile coverings are usually not waterproof in themselves and for wet rooms etc. must therefore be supplemented with a waterproof membrane under the tiling if a substrate of plywood or other moisture-sensitive material is used.

Ceramic tiles that are EN-classified must in accordance with EN 87 (Ceramic floor and wall tiles - Definitions, classification and marking) meet specific requirements for dimensions and surface quality tested in accordance with EN ISO 10545-2 (Ceramic tiles - Determination of dimensions and surface quality).

In addition, tiles are classified according to manufacturing method and water absorption. For the latter, the classes are used:

Tiles for floors should not normally have a water absorption greater than 10%. For wet rooms with underfloor heating, the water absorption should be below 6%.

Determination of other properties takes place in accordance with EN ISO 10545 part 3 to 17. The properties include:
• Sampling.
• Breaking strength.
• Linear thermal expansion.
• Resistance to thermal shock.
• Resistance to cracking.
• Resistance to chemicals.
• Wear resistance.
• Frost resistance.
• Moisture expansion.
• Release of lead and cadmium.
• Walking safety.
• Color deviation.

Hardness (Mohs scale) is tested according to EN 101. Description of tiles within the individual classes can be found in EN 121, EN 159, EN 176, EN 177, EN 178, EN 186, EN 187 and EN 188. These standards also contain the requirements the above-mentioned properties are met. As far as possible, tiles from the same batch with the same shade numbers should be used to ensure a uniform appearance. Some tiles - especially hard-fired porcellanato (stoneware) - are carried in different caliber numbers, i.e. the tiles are sorted after firing according to size in millimetres, which ensures that they can be used together where jointing is desired or if different formats or colors are to be mixed. During the design, the choice of tiles and the determination of the structure should be made in accordance with the expected function of the floor and the resulting effects of use.

In connection with receiving control, it should be checked that the delivery is correct with regard to type, formats, color (shades) and calibre. Complaints about incorrect delivery will generally not be accepted after installation. The delivery must not be defective, i.e. the packages must be undamaged and the individual tiles whole with undamaged edges etc. Laying

A tiled floor must be fully supported by a load-bearing sub-floor. As tiles are inelastic, the subfloor must not undergo significant deformations, and it must therefore have great rigidity and dimensional stability to prevent cracking. The subfloor must be dimensioned according to the expected load, and rolling traffic must also be taken into account; in this connection, requirements must also be made for the flexural strength of the tiles.

Many different materials can be used as a substrate for tiled floors:
• Concrete, lightweight concrete, screed (mortar), anhydrite, etc.
• Wooden boards, gypsum boards.
• Old tiles or terrazzo.
Concrete and screed shrink during curing and will thereby affect the tiling so that compressive stresses occur in the tiles. The shrinkage depends on the concrete composition, layer thickness, temperature and moisture conditions. The shrinkage of the concrete develops most strongly in the relatively young concrete and tiling should therefore be carried out as late in the construction process as possible.

In practice, the shrinkage of normal-hardening cement types at a temperature of approx. 20°C is considered to be over after 4-8 weeks depending on concrete composition, temperature etc. The time between casting and tiling can possibly be reduced by using cement types that have a faster curing process, for example cement types with unpainted lime filler generally have a faster curing process than normally hardening cement types. The best curing conditions are achieved by covering the concrete with tight-fitting plastic film immediately after pouring and maintaining the covering for at least 3 days.

By using plastic foil instead of curing membranes, the best conditions are achieved for later adhesion of screed mortar, tile adhesive, etc. Substrate of anhydrite must be dry - about measurement of moisture content see chapter 2. Before laying tiles, surface mud must be sanded off and subsequently the surface must be primed according to the laying instructions from the supplier of the tile adhesive. For subfloors made of anhydrite, plasterboard and wooden boards, there must be no risk of future moisture influence, i.e. such substrates should only be used in dry environments.

Subfloors made of wooden boards for use with tiles must have a smaller support distance than for flexible floor coverings, for example it can be made of 19 mm structural plywood or 22 mm chipboard with a support distance of 300 mm. Plasterboards must be made with support according to the supplier's instructions. Please note that in wet rooms there are specific requirements for the substrate, which i.a. means that chipboard or plasterboard may not be used as a substrate for tiles.

When laying tiles on top of an existing tiled floor, the existing tiles must be fixed and clean. Laying must be done in strict accordance with the instructions from the supplier of the tile adhesive, including the surface must be primed before laying if the supplier prescribes it. In wet rooms, according to the drainage standard, floor drains must be led unbroken to the surface of the floor, and existing tiling therefore cannot be immediately maintained without replacing the drain (or raising it with a VA-approved extension piece). Please note that the grate frame of the floor drain is considered an integral part of the drain and therefore must not be separated from the rest of the drain bowl. Laying tiles on floating sub-floors should only be done when the sub-floor consists of moisture-stable materials, e.g. concrete. In order to achieve the necessary adhesion, the substrate must be coherent and of sufficient strength, as well as completely clean and free of cement sludge. A mechanical cleaning may be necessary.

Screed layer on slip layer
Leveling layers for tiles can be carried out on sliding layers for sound engineering reasons or to reduce the effect of dimensional changes in the subfloor. The sliding layer can, for example, consist of 2 layers of 0.15 mm plastic foil, or a layer of geotextile and a layer of plastic foil, which is laid out between the subfloor and screed. It is a prerequisite that the subfloor is completely flat and without burrs so that the sliding layer is not destroyed. Traditionally, screeds are made of cement mortar, which must have a minimum thickness of 50 mm, while thicknesses down to 35 mm can be used with special mortars. Laying methods

Previously, it was necessary to lay tiles in mortar. The thickness of the tiles varied and therefore a relatively thick layer of mortar had to be used. Today, there is a large selection of tile adhesives, so there are now far more options for choosing a laying method. A distinction can be made between laying with tile adhesive (the thin layer method) and laying in mortar (the mortar method). Before laying tiles, switch off any underfloor heating system at least 3 days before laying and it must be switched on again no earlier than 3 weeks after laying.
Before laying, spread a number of tiles - preferably approx. 3 m² - onto the floor to ensure an aesthetically satisfactory result. When laying, tiles from different packages/boxes are mixed. These precautions are particularly important for tiles where color nuances can be expected, e.g. where natural colors have been used. The tiles must not be made wet before laying. For natural stone, possibly moisture causes the tiles to curve after laying - causes "bread crust" on the surface.
Tile adhesive
Tile adhesive (the thin layer method) is applicable to flat surfaces and tiles of uniform thickness. The substrate must normally have a flatness corresponding to a tolerance of ± 2 mm on a 2 m straight beam. If the substrate is too uneven, it must be created either with a mortar/putty compound that is adapted to the substrate, or with a sheet covering that is suitable for the purpose. In the thin-layer method, a tile adhesive is used which is usually cement-based, and which may have added plasticizers and plastic binders (dispersion liquids e.g. based on acrylic) to improve adhesion, tightness, flexibility, etc.

Products from the same supplier should be used for all sub-operations, which gives the greatest certainty that the materials can be used together, as well as being an advantage in terms of any guarantees or complaints. Choice of tile adhesive, primer, etc. must be done depending on the actual tile and especially the actual substrate, which may have different properties in terms of deformations as a result of shrinkage and temperature and moisture variations. For substrates made of wood-based board materials, it is particularly important to take moisture movements into account, while for concrete it is especially important to take into account shrinkage, i.e. the composition of the concrete and especially its age.

For light stone materials, e.g. marble, light/white tile adhesive should be used as the color can show through from the substrate. If marble can be discolored by moisture or due to the content of iron compounds, a fast-hardening tile adhesive should be used when laying. Green marble can be particularly problematic and it is recommended that laying takes place in strict accordance with the instructions from both the tile and adhesive supplier. When laying, the temperature must be at least 10°C. After laying, the floor must not be exposed to rapid drying, e.g. from strong sun, drafts or heat guns. It is important that the correct amount of tile adhesive is used depending on the substrate, the tile and the chosen type of adhesive. Too little adhesive will result in poor filling and insufficient coverage and the risk of poor adhesion. Too much adhesive entails the risk of poor flatness of the finished floor surface and the adhesive penetrating into the joints during installation.

The consumption of adhesive is regulated using the tooth size selected on the notched trowel. You can choose between toothed spatulas with square teeth or semi-round teeth. With square teeth, the putty size is chosen according to the unevenness of the tile, while for half-round teeth, it is chosen according to the total unevenness of the substrate and tile. Floating/buttering, which means that adhesive is applied to both the substrate and the tile, is used for very large tiles, outdoors, for swimming pools and similar places where it is important that there are no air bubbles in the adhesive layer.

There are no fixed rules for how much tile adhesive is needed, but the following guidelines can be given for choosing a toothed putty:

As an example of consumption, it can be mentioned that with a tooth size of 10x10 mm, the consumption is usually approx. 4.5 kg/m² and with 3x3 mm notched trowel approx. 1.6 kg/m².

Tile adhesive must not be applied to larger areas than the tiles can be laid before the laying mortar forms a skin, as this will result in poor adhesion. If skin has formed, the tile adhesive must be replaced with fresh adhesive.

The mortar method or the thick film method
The mortar method is also applicable on uneven surfaces and tiles of uneven thickness. Below is a general description of the method and products.
For concrete product selection, refer to the suppliers' instructions. Adhesion to the substrate must be good and it must be ensured that no significant deformations of the substrate occur. It may therefore be necessary to create the substrate before laying the tiles, just as any drop in the floor should be done in the substrate. Before laying, water the substrate and keep it moist for approx. 1 day. Immediately before the laying mortar is applied, coat the substrate with cement slurry C 100/100, optionally with added concrete adhesive. Larger areas must not be carried out than the cement slurry is constantly moist.

The laying mortar should be a C 100/400 to C 100/500. It should be as stiff as possible and laid out and compacted to the right thickness so that full contact between tile and mortar can be achieved. When the laying mortar has been laid out, a thin layer of cement slurry C 100/100 is poured onto the surface, on which the tile is laid down and tapped into place. The best curing conditions are achieved by covering the tiles with plastic film for the first 2 days after laying, optionally supplemented with a layer of moist sacks between the tiles and plastic film. Joints
Joints are an essential part of a tiled floor. The joints should ideally be able to absorb the same impacts as the tile itself and should support the tile edges. They must also be able to distribute the forces that appear in the floor, so that large local stress concentrations do not occur that could cause damage. Generally, cement-based joint mortars are used. For special purposes, there are special products, e.g. acid-resistant or flexible joint mortars. The joint width can vary between 0 and 25 mm and is chosen according to the requirements of the floor construction as well as the format, tolerances, rusticity of the surface of the tiles used and the desired appearance of the floor. The widest joints are often used for large and rustic tiles. Should the floor be laid with a crack joint, i.e. close together so that the joint does not have to be grouted, it can possibly be sanded after laying, and in the case of natural stone tiles water sanded. It is recommended to use tiles with slightly bevelled edges for floors with crevice joints to prevent the edges from breaking off and so that sharp edges do not appear on the floor surface.
Grouting should normally be done no earlier than 1-3 days after tiling, depending on the laying method/type of adhesive and substrate. Before grouting, the joints are moistened lightly with a sponge, but without standing water in the joints. For tiles laid in tile adhesive, special joint mortars are normally used, which can be adapted to the type of tile used in terms of colour, "roughness" etc. Tiles laid in mortar can also be grouted with grout, but grouting can also be done in the traditional way, e.g. with cement mortar C 100/100. For certain industrial floors and other special applications, it may be necessary to grout with special mortar, e.g. on an epoxy basis. It should be avoided as far as possible to choose dark joints for completely light floors, due to the risk of dye contamination to the tile. Smaller variations in the joint's color and surface structure may occur due to different absorbency of tiles and substrates. The floor should be put into use 2-3 days after tiling at the earliest.
Expansion joints
Sufficient expansion joints must be installed to prevent damage to the floor due to deformations in the construction or uneven movements of the coating and substrate. The location and construction of expansion joints is usually determined during the planning process. Normally, expansion joints must go completely through the construction, including screed etc. Where only small movements are expected, e.g. in limited areas above beams etc., expansion joints in the tiling itself are however sufficient. Expansion joints made as sealant joints should, as a general rule, be 10-15 mm wide. Expansion joints must be free of tile adhesive/mortar in the entire cross-section and a bond-breaking joint underlay or a release tape should be placed at the bottom of the joint. An elastic sealant joint is used as joint material, e.g. MS polymer or silicone, which in wet rooms should have a fungicide (algae killer) added to it. In the case of walls and columns etc., the joint width can possibly be reduced.

In industrial floors, swimming pools and commercial kitchens, there may be special requirements, e.g. about slip resistance, which should be documented by the supplier. In connection with natural stone floors, the use of sealant joints based on oil products can in some cases lead to penetration of oil/dyes into the tile. Information should be sought from the supplier on whether the use of current products is associated with risk in this respect. Where larger movements are expected or where the edges of the tiles must be reinforced around the joint due to heavy loads, special joint profiles can be used, which are usually made of metal with embedded rubber profiles.
Expansion joints should, as a general rule, be carried out according to the following guidelines:
• Largest rectangular area without expansion joints approx. 35 m².
• Maximum distance between expansion joints approx. 7 m - this distance is reduced to 5 in connection with underfloor heating
• In the case of expansion joints or moldings in the load-bearing structure, expansion joints must also be made in the tiling, including any screed. m.
• It must be clear from the description or drawings where floor bending may occur and therefore expansion joints must be established, for example where deck elements are laid out on beams that are stiffer than the deck elements themselves.
• Where only parts of a larger floor area are covered with tiles, this should be delimited with expansion joints against adjacent floors.
• Where expansion joints are necessary, expansion joints (insulation joints) must also be made against adjacent walls, columns and the like.
• Expansion joints performed as sealant joints must be performed with adhesive-breaking joint backing or release tape. Wet room
In wet rooms, tiled floors must be installed according to the guidelines set out in the Norwegian Building Research Institute's instructions for the area, i.e. SBi Instruction 252 "Wet rooms" as well as SBI instructions 180 and 189. If the floor is made as a light construction, i.e. with a construction plywood subfloor, a waterproof membrane must always be installed, which must be carried at least 100 mm up all adjacent walls. The waterproofing system must be carried out as directed in the above publications and in strict accordance with the tile adhesive supplier's MK approval. If the floor is laid on an inorganic surface, e.g. a concrete deck, tiles can be laid directly on the deck. However, it is recommended that a waterproof membrane is always installed, especially in the most water-stressed parts of the room, e.g. in and around the shower niche. Underfloor heating
Underfloor heating systems are suitable in connection with tiled floors and are chosen partly to achieve better comfort and partly to avoid radiators.

When using underfloor heating systems, there are two prerequisites that must be met:
The temperature must be low - normally the surface temperature should not exceed 27-29°C. The temperature distribution under the tiles must be even, i.e. heating pipes or cables must be placed so that there are no major variations in the surface temperature. An even temperature distribution is achieved most cheaply by embedding heating pipes or heating cables in a concrete or screed layer. Above pipes or cables, there should be a concrete thickness of at least 30 mm to achieve an even distribution of the temperature. Alternatively, the underfloor heating system can be made with heating mats or heating foils, whereby the thickness of the casting can be reduced. Please note that floors with electric heating may only be installed in single rooms in connection with renovations or in summer houses.

With floor heating, it is difficult to regulate the heat release quickly due to the thermal inertia of the concrete floor, which means that the time constant for floors of this type is approx. 12 hours. On floors made of wood-based boards, underfloor heating systems should only be used in connection with the laying of a leveling layer laid on a sliding layer, e.g. of 2 layers of 0.15 mm plastic foil. This is because wooden panels undergo large dimensional changes when drying out and moistening, which can cause the tiles to crack. Underfloor heating systems should be equipped with their own heating circuit and automation to limit the temperature under the floor. The surface temperature limits the effect that an underfloor heating system can provide.

As a guide, it can be assumed that underfloor heating systems can produce an effect which can be calculated according to the formula below:
Output power = 11 x (tg - tr) W/m².

Where tg is the surface temperature of the floor and tr is the room temperature where the most common surface temperatures correspond to the values shown in table 1.

Table 1. Delivered power for tiled floors for commonly occurring surface temperatures at a room temperature of 21°C.

For comparison, it can be stated that the energy requirement for new single-family houses insulated according to BR-S 98 is 45 W/m². Heating with underfloor heating can therefore be expected to be sufficient in new, well-insulated buildings. For renovation tasks, as a general rule, it must be expected that there must be supplementary heat supply in addition to the underfloor heating system, for example in the form of radiators. This is because the insulation in older houses is usually inferior to the current requirements, and the power requirement is correspondingly greater. In general, greater energy consumption is to be expected when using underfloor heating systems than with radiator systems. This is the reason why in BR-S 98 there are stricter insulation requirements for off-road decks, basement floors against the ground and floor separations (above the open or above ventilated crawl space) with underfloor heating. Cleaning
Cleaning Before commissioning, a basic cleaning is carried out to remove residues of joint mortar/limestone from the surface of the coating. The future users must be informed about correct cleaning as incorrect cleaning can cause damage to the surface. Dry methods can be used for daily cleaning, i.e. dry or wet mopping or vacuuming. Both alkaline and acidic cleaning agents are used for stronger cleaning. However, acid cleaning agents must not be used on basalt, marble and other lime-based natural stones, as this will break down the surface. Furthermore, most joint mortars will be cement-based and therefore cannot withstand strong or prolonged exposure to acidic cleaning agents.

Finally, tiled floors can be cleaned by foam cleaning, provided that they are laid on an inorganic substrate and that the tile adhesive and grout can withstand it. Cleaning by pressure washing should only be done to an extremely limited extent, with moderate pressure and only when materials have been used which the suppliers describe as suitable for the purpose. Checklist when choosing tiled floors

• Conditions regarding construction, choice of materials, placement and execution of expansion joints, etc. must be clarified before laying begins.
• The building must be closed and before laying on wooden boards the heating system must be started and the building must be in moisture equilibrium with the surroundings.
• Supplier instructions must be available on the construction site.
• When laying with tile adhesive, materials (tile system) from the same supplier should be used.
• Substrates of concrete or mortar must be well hardened and most of the shrinkage must be over.
• The underfloor heating system is switched off at least 3 days before installation and must be switched on again no earlier than 3 weeks after installation.
• The temperature must be at least 10°C. Lower temperatures extend the curing time for screed, tile adhesive and grout.
• The moisture content of wooden boards must be below 13%.
• Substrates must be solid, clean, dry and free of burrs, lumps, casting sludge, etc. If necessary, the surface must be cleaned and/or straightened.
• Tile adhesives, sealants and other auxiliary substances should be acclimatised in terms of temperature for at least a day before use, for example when storing in the rooms in which they are to be used.